Human Exploration of Phobos Andrew F. J. Abercromby Michael L. Gernhardt Steven P. Chappell Wyle Science, Technology and National Aeronautics and Wyle Science, Technology and Engineering Group Space Administration Engineering Group Wyle/HAC/37C 2101 NASA Parkway Wyle/HAC/37C 2101 NASA Parkway Houston, TX 77058 2101 NASA Parkway Houston, TX 77058 [email protected] Houston, TX 77058 [email protected] [email protected] David E. Lee A. Scott Howe National Aeronautics and Jet Propulsion Laboratory Space Administration 4800 Oak Grove Dr. 2101 NASA Parkway Pasadena, CA 91109 Houston, TX 77058 [email protected] [email protected] Abstract—This study developed, analyzed, and compared system) and as an EVA platform, both on Phobos and for mission architectures for human exploration of Mars’ moons contingency EVA on the Mars transit habitat. within the context of an Evolvable Mars Campaign. CONCLUSIONS: Human exploration of Phobos offers a METHODS: All trades assumed conjunction class missions to scientifically meaningful first step towards human Mars Phobos (approximately 500 days in Mars system) as it was surface missions that develops and validates transportation, considered the driving case for the transportation architecture. habitation, and exploration systems and operations in advance All architectures assumed that the Mars transit habitat would of the Mars landing systems. remain in a high-Mars orbit (HMO) with crewmembers transferring between HMO and Phobos in a small crew taxi TABLE OF CONTENTS vehicle. A reference science/exploration program was developed including performance of a standard set of tasks at 1. INTRODUCTION ................................................. 1 55 locations on the Phobos surface. Detailed EVA timelines 2. PHOBOS MISSION ARCHITECTURE CASES AND were developed using realistic flight rules to accomplish the reference science tasks using exploration systems ranging from ASSUMPTIONS................................................... 2 jetpacks to multi-person pressurized excursion vehicles 3. EXPLORATION SYSTEMS CONCEPTUAL combined with Phobos surface and orbital (L1, L4/L5, 20 km DEVELOPMENT AND DOWN-SELECT................ 3 distant-retrograde-orbit [DRO]) habitat options. Detailed models of propellant mass, crew time, science productivity, 4. REFERENCE SCIENCE / EXPLORATION radiation exposure, systems and consumables masses, and REGIONS, SITES, AND TASKS ........................... 8 other figures of merit were integrated to enable quantitative 5. PHOBOS SURFACE TRANSLATIONS .................. 9 comparison of different architectural options. Options for prestaging assets using solar electric propulsion versus 6. EVA TIMELINES ............................................. 10 delivering all systems with the crew were also evaluated. Seven 7. COMPARISON OF MISSION ARCHITECTURES . 11 discrete mission architectures were evaluated. RESULTS: The 8. CONCLUSIONS ................................................. 14 driving consideration for habitat location (Phobos surface versus orbital) was radiation exposure, with an estimated REFERENCES ....................................................... 15 reduction in cumulative mission radiation exposure of up to BIOGRAPHY ........................................................ 17 34% (versus a Mars orbital mission) when the habitat is located on the Phobos surface, compared with only 3% to 6% reduction for a habitat in a 20-km DRO. The exploration 1. INTRODUCTION utility of lightweight unpressurized excursion vehicles was limited by the need to remain within 20 minutes of solar Human exploration missions to the moons of Mars have particle event radiation protection combined with complex been proposed as an intermediate step for eventual Mars guidance, navigation, and control systems required by the surface missions [2, 3]. As explained by Korsmeyer et al. nonintuitive and highly-variable gravitational environment. [4], human missions to Mars’ moons would result in the Two-person pressurized excursion vehicles as well as mobile development and operation of new technologies, systems, surface habitats offer significant exploration capability and operational benefits compared with unpressurized and ops concepts, many of which will be required for extravehicular activity (EVA) mobility systems at the cost of eventual Mars surface missions, without the added increased system and propellant mass. Mechanical surface complexity and risk associated with Mars descent, ascent, translation modes (ie, hopping) were modeled and offered and long-duration surface systems and operations. The potentially significant propellant savings and the possibility of opportunity to perform low-latency teleoperation (LLT) of extended exploration operations between crewed missions. robotic Mars surface systems could provide significant Options for extending the use of the crew taxi vehicle were benefits not only for scientific exploration purposes, but examined, including use as an exploration asset for Phobos also in the scouting and preparation of landing sites in surface exploration (when combined with an alternate mobility U.S. Government work not protected by U.S. copyright 1 advance of human surface missions [4, 5]. The manufacture, selected for use within the seven overall mission transportation, and transfer of propellant, oxygen (O2), architectures. The representative regions of scientific and/or other products produced via in-situ resource interest, subsites, and standard set of scientific exploration utilization (ISRU) on the Mars surface could significantly tasks used in this study are described in Section 4. Section 5 decrease the mass that must be landed to support human describes analysis of Phobos surface translation techniques surface missions; however, these tasks are complex, mission and Delta-V requirements that were incorporated into an critical, and in some cases must be performed before any integrated model along with crew time and consumables human landings have occurred. The capability to perform estimates from detailed EVA timelines, which are described low-latency teleoperations in support of ISRU could in Section 6. Results of the quantitative comparison of mitigate some of the associated risks and decrease the level mission architectures are presented and discussed in Section of autonomy required of the ISRU systems [5]. Although 7 along with a qualitative assessment of the potential for Phobos and Deimos differ significantly from each other commonality and evolvability of the Phobos mission with respect to the latitudes, duration, and frequency with architecture elements within the EMC. Conclusions are in which line-of-sight to Mars is achievable, both moons offer Section 8. frequent and operationally useful periods of time and latitudes within which low-latency teleoperations of Mars 2. PHOBOS MISSION ARCHITECTURE CASES AND surface assets could be performed [6]. Selection of specific ASSUMPTIONS landing sites on each moon and/or use of communication relays would further increase teleoperations capabilities. This paper describes the results of a single phase of study of Low-latency teleoperations may also include collection and Mars mission architectural options within the EMC launch of Mars samples into Mars orbit for retrieval and framework. All trades assumed conjunction class missions return as part of a human mission to Mars’ moons. to Phobos (330 to 550 days in Mars system) as it was considered the driving case for the transportation The aforementioned benefits of a human mission to Mars’ architecture. The HAT is undertaking more detailed analysis moons can also be said of human Mars orbital missions or of Phobos and Deimos mission architectures at the time of even, to a lesser extent, a Mars fly-by mission [4]. Indeed, writing. Ongoing work also includes analysis of human for the purposes of this study, it is assumed that assisted sample return options and development and testing crewmembers are first transported in a Mars transit vehicle of LLT systems and ops concepts. (MTV) on a conjunction class trajectory and inserted into a one-sol high-Mars orbit (HMO) where the MTV would Mission Architecture Cases remain until the Earth-return transit is initiated. The primary benefits of then sending crewmembers from HMO to Seven mission architecture cases are summarized in this Phobos or Deimos in a smaller crew-taxi spacecraft are that section and shown in Table 1. Detailed explanations of the 1) meaningful scientific exploration of Mars’ moons can /be exploration systems and down-select process that resulted in performed by humans [4, 7] and 2) the radiation dose to the seven mission architectures are provided in Section 3. which crewmembers are exposed may be significantly reduced compared with HMO because of the shielding Table 1 – Mission Architecture Cases A-G. PEV is the effect of the moons [6]. pressurized excursion vehicle, described below and in Section 3. This paper describes a study to systematically develop, analyze, and compare several different human Phobos mission architectures within the context of the Evolvable Mars Campaign (EMC) [8] being developed by NASA’s Human Spaceflight Architecture Team (HAT). Specifically, architectures were evaluated that incorporated different crew sizes, mission durations, crew taxi concepts, habitat concepts and locations, and EVA mobility systems. Figures of merit focused on radiation dose, scientific exploration productivity, and mass estimates of systems, propellant, and